The tribology of laminated magnetic recording heads

This thesis investigates the mechanisms that lead to pole tip recession (PTR) in laminated magnetic recording heads (also known as "sandwich heads"). These heads provide a platform for the utilisation of advanced soft magnetic thin films in practical recording heads suitable for high frequency helical scan tape recording systems. PTR results from a differential wear of the magnetic pole piece from the tape-bearing surface of the head. It results in a spacing loss of the playback or read signal of 54.6dB per recording wavelength separation of the poles from the tape. PTR depends on the material combination used in the head, on the tape type and the climate - temperature and relative humidity (r.h.). Five head materials were studied: two non-magnetic substrate materials- sintered multi granular CaTi03 and composite CaTi03/ZrTi04/Ti02 and three soft magnetic materials- amorphous CoNbZr, and nanocrystalline FeNbSiN and FeTaN. Single material dummy heads were constructed and their wear rates measured when cycling them in a Hi-8 camcorder against commercially available metal particulate (MP) and metal evaporated (ME) tapes in three different climates: 25°C/20%r.h., 25°C/80%r.h. and 40°C/80%r.h. X-ray photoelectron spectroscopy (XPS) was used to examine changes the head surface chemistry. Atomic force microscopy (AFM) was used to examine changes in head and tape surface topography. PTR versus cycling time of laminated heads of CaTi03/ZrTiO4/Ti02 and FeTaN construction was measured using AFM. The principal wear mechanism observed for all head materials was microabrasion caused by the mating body - the tape surface. The variation in wear rate with climate and tape type was due to a variation in severity in this mechanism, except for tape cycling at 40°C in which gross damage was observed to be occurring to the head surface. Two subsidiary wear mechanisms were found: third body scratching (all materials) and grain pullout (both ceramics and FeNbSiN). No chemical wear was observed, though tribochemical reactions were observed on the metal head surfaces. PTR was found to be caused by two mechanisms - the first differential microabrasion of the metal and substrate materials and which was characterised by a low (~10nm) equilibrium value. The second was by deep ploughing by third body debris particles, thought mainly to be grain pullout particles. This level of PTR caused by this mechanism was often more severe, and of a non-equilibrium nature. It was observed more for ME tape, especially at 40°C/80%r.h. and 25°c/20%r.h. Two other phenomena on the laminated head pole piece were observed and commented upon: staining and ripple texturing.

Modulation of certain 5-HT-related behaviours by serotonergic and noradrenergic systems

The modulation of 5-hydroxytryptamine (5-HT)-related head-twitchbehaviour by antimigraine drugs and migraine triggers was examined inmice. The antimigraine drugs examined produced either inhibition or noeffect on 5-HT-related head-twitching. On the basis of these resultsit is suggested that 5-HT-related head-twitching is unlikely to beuseful in the preclinical screening and discovery of systemically-activeantimigraine agents. The migraine triggers examined, tyramineand beta-PEA initially produced a repeatable complex time-relatedeffect on 5-HT-related head-twitching, with both inhibition andpotentiation of this behaviour being observed, however, when furtherexamination of the effect of the migraine triggers on 5-HT-relatedhead-twitching was attempted some time later the effects seeninitially were no longer produced. The effect of (±)-1-<2, 5-dimethoxy-4-iodophenyl)-2-aminopropane,((±)DOl), on on-going behaviour of mice and rats was examined. Shakingbehaviour was observed in both species. In mice, excessive scratchingbehaviour was also present. (±)DOl-induced scratching and shakingbehaviour were found to be differentially modulated by noradrenergicand serotonergic agents, however, the fact that both behaviours wereblocked by ritanserin (5-HT2/5-HT1c receptor antagonist) and inhibitedby FLA-63 (a dopamine-beta-oxidase inhibitor which depletesnoradrenaline), suggests the pathways mediating these behaviours mustbe convergent in some manner, and that both behaviours require intact5-HT receptors, probably 5-HT2 receptors, for their production. Ingeneral, the behavioural profile of (±)DOI was as expected for anagent which exhibits high affinity binding to 5-HT2/5-HT1c receptors.Little sign of the 5-HTl-related '5-HT syndrome' was seen in eithermice or rats. The effect of a variety of noradrenergic agents on head-twitchinginduced by a variety of shake-inducing agents was examined. A patternof modulatory effect was seen whereby the modulatory effect of thenoradrenergic agents on 5-hydroxytryptophan <5-HTP) (and in some cases, 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)) was found to be the opposite of that observed with quipazine and (±)DOI. The relationship between these effects, and their implications for understanding the pharmacology of centrally acting drugs is discussed.

Cross-linking of cellular proteins by tissue transglutaminase during necrotic cell death:a mechanism for maintaining tissue integrity

Tissue transglutaminase (tTG) is a Ca2+-dependent enzyme which cross-links proteins via e(g-glutamyl)lysine bridges. There is increasing evidence that tTG is involved in wound repair and tissue stabilization, as well as in physiological mechanisms leading to cell death. To investigate the role of this enzyme in tissue wounding leading to loss of Ca2+ homoeostasis, we initially used a model involving electroporation to reproduce cell wounding under controlled conditions. Two cell models were used whereby tTG expression is regulated either by antisense silencing in ECV 304 cells or by using transfected Swiss 3T3 cells in which tTG expression is under the control of the tet regulatory system. Using these cells, loss of Ca2+ homoeostasis following electroporation led to a tTG-dependent formation of highly cross-linked proteinaceous shells from intracellular proteins. Formation of these structures is dependent on elevated intracellular Ca2+, but it is independent of intracellular proteases and is near maximal after only 20min post-wounding. Using labelled primary amines as an indicator of tTG activity within these 'wounded cells', we demonstrate that tTG modifies a wide range of proteins that are present in both the perinuclear and intranuclear spaces. The demonstration of entrapped DNA within these shell structures, which showed limited fragmentation, provides evidence that the high degree of transglutaminase cross-linking results in the prevention of DNA release, which may serve to dampen any subsequent inflammatory response. Comparable observations were shown when monolayers of cells were mechanically wounded by scratching. In this second model of cell wounding, redistribution of tTG activity to the extracellular matrix was also demonstrated, an effect which may serve to stabilize tissues post-trauma, and thus contribute to the maintenance of tissue integrity.

The fevered novel from Balzac to Bernanos:frenetic Catholicism in crisis, delirium and revolution

Book Review: The Fevered Novel from Balzac to Bernanos: Frenetic Catholicism in Crisis, Delirium and Revolution. By Francesco Manzini. (IGRS Books). London: Institute of Germanic and Romance Studies, 2011. 264 pp. Full text: This monograph is an important and compelling account of a novelistic tradition that stretches from Georges Bernanos back to Balzac, by way of Léon Bloy, Joris-Karl Huysmans, and Barbey d'Aurevilly. Depending on a master plot that evokes Maistrean themes of blood, sacrifice, and redemption, working in a feverish female body, this canon combines Romantic freneticism and anti-Enlightenment religion to create a compound that Francesco Manzini calls ‘frenetic Catholicism’. The theme of fever, Manzini tells us, was commented on by Huysmans in writing about Barbey d'Aurevilly. When André Gide read Bernanos's Sous le soleil de Satan, he dismissed it as a rehash of Bloy and Barbey. In this present work Manzini aims to make us aware once more of the gradually intensifying themacity of fever in writings more usually classed in theologo-literary categories. His analysis encompasses (though is not restricted to) Balzac's Ursule Mirouët, Barbey d'Aurevilly's Un prêtre marié, Huysmans's En rade, Bloy's Le Désespéré and La Femme pauvre, and Bernanos's Nouvelle histoire de Mouchette. Thus, as Manzini argues in his conclusion, between the freneticism of the Romantics and that of the surrealists this corpus represents an intermediary wave of freneticism, foregrounding fever, hyperconsciousness, dreamlike episodes, and female automatism. Manzini's knowledge of, and ease amidst, the sources is constantly impressive. Much like Richard Griffiths before him (The Reactionary Revolution: The Catholic Revival in French Literature, 1870–1914 (London: Constable, 1966)), he has read both the bad novels and the good ones. For that we are in his debt. His commentary thrives on the oddities of his subjects. He points quite rightly to the peculiar hubris of writers whose contempt for the secular excesses of scientism leads them down a cul-de-sac of primitive medical quackery. Likewise, he underlines how Zola's attempt to unwrite Barbey — exorcising the former's anti-Romantic animus, as much as scratching his anticlerical itch — leads him to recapitulate Barbey's religious authoritarianism in the secular vernacular of patriarchy. Les espèces qui se rapprochent se mangent, to paraphrase Bernanos (Les Grands Cimetières sous la lune). In spite of all Manzini's tightly organized analysis, however, this reader wonders whether the fevered novel ‘best allowed contemporaries — and now […] literary critics and historians — to imagine the issues at stake in the amorphous scientistic, religious, and political debates’ of the period (p. 17). Below the ideological clashes of nineteenth-century science and religion, the two contending dynamics of anthropocentrism and theocentrism are attested and, it can be argued, even more perfectly dramatized in other Catholic literature (Charles Péguy's poetry, for example). In these terms, what distinguishes the Catholic frenetics from their Romantic or surrealist counterparts is that their fevered subject represents an attempt to build a road out of what Canadian philosopher Charles Taylor calls ‘buffered’ individuality, and back towards the theocentric porous subject who is open to divine influence. By way of minor corrections, nuns do not take holy orders (p. 94) but make religious profession by taking vows. Also, the last Eucharistic host is not extreme unction (p. 119) but viaticum.